The purpose of a fraud on a secured terminal consists of attempting to detect confidential information stored in this terminal or entered by a user on such a terminal in order to reuse them to his/her expense.
A known means for fraudulently accessing confidential information entered by the user consists of incorporating spies into the terminal in order to detect the keys pressed by the user.
Incorporating spies into the terminal requires the opening of this terminal.
Solutions have already been proposed for guaranteeing the security of terminals on which confidential information has to be entered.
Document FR 2 815 733 describes a security device for a casing comprising a cap, an electronic card and a flexible membrane on which keys are molded.
The security device comprises a dedicated key of the membrane designated as <<false key>> hereafter.
The security device also comprises two electrically conducting terminals positioned on the electronic card facing the false key and connected to processing means of the casing.
The false key includes at its base an electrically conducting portion which faces both terminals.
In a normal operating condition of the casing, the false key is maintained pressed down with a determined force in order to close an electric circuit for detecting intrusion.
The opening of the casing by a third party for inserting spies therein induces an opening of the electric detection circuit caused by the release of the false key.
This opening of the circuit is detected by processing means of the device which activates anti-fraud functions of the casing, as for example shutdown of the casing or even deletion of confidential data.
However, a drawback of this type of device is that it does not comprise any means for protecting the false key against possible hacking.
Thus, a malevolent third party who manages to short-circuit the false key makes the security device inoperative, so that a subsequent opening of the casing is not detected and does not cause activation of the anti-fraud functions of the casing.
An object of the present invention is to propose an improved device for protection against intrusions of electronic devices containing a keyboard for entering confidential data.